Glossary | U – Z (The vocabulary of the coating and heat-treating industries—explained)

Back to Main Page A B C D E F G H I J K L M N O P Q R S T U V W X Y Z



An NDE technique wherein an ultrasonic beam passes through a coating and substrate and provides a signal from the back wall. The signal is detectable by a sensor. The height of this backwall echo depends on the discontinuity in impedance from the sprayed coating to the substrate. Bonding flaws can be easily seen by the weakening of the back wall echo.


A synonym for supercooling.


In castings, the removal and repair of discontinuities to raise the quality level of the casting beyond that which can be economically achieved by good foundry practice.


Vacuum Annealing

Annealing carried out at subatmospheric pressure.

Vacuum Carburizing

A high-temperature gas carburizing process using furnace pressures between 7 and 55kPa during the carburizing portion of the cycle.

Vacuum Casting

A casting in which metal is melted and poured under very low atmospheric pressure; a form of permanent mold casting where the mold is inserted into liquid metal, vacuum is applied, and metal drawn up into the cavity.

Vacuum Coating

The deposition of thin films and coatings using a vacuum environment and an atomic or molecular condensable vapor source. The vacuum environment reduces gas particle density, limits gaseous contamination, establishes partial pressures of inert and reactive gases and controls gas flow. The gaseous environment can be partially ionized plasma, and the vapor source can be of PVD or CVD.

Vacuum Furnace

A furnace that uses low atmospheric pressures instead of the protective gaseous atmosphere used by most heat-treating furnaces. They are categorized as hot wall or cold wall depending on the location of the heating and insulating components.

Vacuum Nitrocarburizing

A subatmospheric nitrocarburizing process that uses a basic atmosphere of 50% ammonia / 50% methane, containing controlled oxygen additions of up to 2%.

Vacuum Plasma Spraying

Plasma spraying carried out in a chamber which has been evacuated to a low partial pressure of oxygen. It is then usually partially backfilled with argon to avoid the possibility of forming a glow discharge.

Vanadium (V)

A chemical element, atomic number 23, which inhibits grain growth during heat treatment and which improves the strength and toughness of hardened and tempered steels. Additions up to .05% increase hardenability, whereas larger amounts tend to reduce hardenability due to the formation of carbide. It is also utilized in ferrite/pearlite microalloy steels to increase hardness through carbonitride precipitation strengthening of the matrix.

Vector Plot

A way of displaying results from a CFD analysis, where the velocity of each particle is visualized with an arrow. Since the arrow represents velocity it has a direction and magnitude (the length of the arrow indicates the relative magnitude).


A discontinuity on the surface of a casting—appearing as a raised, narrow, linear ridge—that forms upon cracking of a sand mold or core caused by the expansion of the sand during the filling of the mold with molten metal.

Vickers Hardness Test

A microindentation hardness test that employs a 136° diamond pyramid indenter (Vickers) and variable loads—enabling the use of a single hardness scale, the range of which spans from very soft lead to tungsten carbide. Also known as the diamond pyramid hardness test.


Walking-Beam Furnace

A continuous-type furnace consisting of two sets of rails, one stationary and the other movable. Only the work being processed has to be heated because trays or fixtures are not needed.


Deformation other than contraction that develops in a casting between solidification and room temperature; also, distortion occurring during annealing, stress relieving, and high-temperature service.


A casting defect resulting from erosion of sand by metal flowing over the mold or corded surfaces. It appears as rough spots and excess metal on the casting surface. Also called cuts.

Washburn Core

A thin core which constricts the riser at the point of attachment to the casting. The thin core heats quickly and promotes feeding of the casting. Riser removal cost is minimized.

Water Quenching

A quench in that uses water as its quenchant. The major disadvantage of water quenching is its poor efficiency at the beginning, or hot stage, of the quenching process.


Loss of material from a surface by means of relative motion between it and another body.


A process used to join metals by the application of heat. Fusion welding, which includes gas, arc, and resistance welding, requires that the parent metals be melted.

Welding Electrode

A metal or alloy in rod or wire forms used in electric arc welding to maintain the arc and at the same time supply molten metal or alloy at the point where the weld is to be accomplished.

Welding Flash

Skin exposed too long to the ultraviolet rays of welding or melting arcs will burn as in a sunburn. Though temporary blindness can result, it is not permanent, as is popularly believed.

Welding Stress

That stress resulting from localized heating and cooling of metal during welding.

White Layer

A compound layer that forms as a result of the nitriding process.

Wire Spraying

A thermal spray process whereby the supply for the coating material is fed into the gun in the form of a continuous wire.

Work Hardness

Hardness developed in metal; the result of cold working.


X-Ray Diffraction (XRD)

A surface science technique for crystalline structure analysis of materials. Widely used both in the research and industrial area. Analyzed depth: up to 10 micrometers.

X-Ray Photoelectron Spectroscopy (XPS)

An electron beam technique applied for the identification of near-surface elements and the analysis of chemical state. Widely used in thin film science. Analysis depth: a few Angstroms.


Yield Point

The lowest amount of stress in a material at which an increase in strain occurs without an increase in stress. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The yield point is usually less than the maximum attainable stress.

Yield Strength

The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2% is used for many metals. Compare with tensile strength.


Zinc (Zn)

A metallic, chemical element (atomic number 30) that provides galvanic corrosion protection when applied as a coating.

Zinc Plating

The electrodeposition of zinc or zinc alloys (e.g. Zn/Ni, Zn/Sn) to provide galvanic corrosion protection.

Back to Top